International Journal of Marine Science, 2025, Vol.15, No.3, 154-166 http://www.aquapublisher.com/index.php/ijms 158 genes also increases, suggesting that ecdysterone may play a promoting role in ovarian development. In male shrimp, testicular development involves spermatogenesis and spermatopod formation. Supporting cells in the semen secrete a variety of factors that affect spermocyte meiosis, with some of the key regulatory genes derived from the gender-determining pathway (Alfaro-Montoya, 2010). By comparing gonad transcriptomes at different developmental stages, dynamic patterns of reproductive genes can be observed. For example, when the gonads of the larval shrimp are not differentiated, the expression of genes related to gametegenesis is very low; during the gonad differentiation and maturation stage, these genes (such as Cyclin related to meiosis, etc.) are rapidly activated, and their expression peaks correspond to the rapid gamete proliferation stage. 4.2 Research on the mechanism of differentiation between male and female and gender determination (such as Dmrt, Foxl2) Crustaceans have complex and diverse gender-determining mechanisms. Most economic shrimps are dioecious and have male and female dimorphs. Unlike mammals that are dominated by sex chromosomal genes (SRYs), crustaceans often control gender differentiation by hormones secreted by male islets (also known as male glands, endocrine organs unique to males). The insulin-like androgen hormone (IAG) produced by male islets is considered a switch: as long as the male shrimp larvae produces IAG, the male differentiation pathway will be initiated; if several IAG signals are disturbed, the individual will develop into a female or a male-female interferometer (Yang et al., 2020). In recent years, some conservative regulators involving gender differentiation have also been found in freshwater shrimp. The Dmrt gene family and the Foxl2 gene are thought to play roles similar to the determinants of vertebrate gonads in invertebrates. Xu et al. (2022) cloned and analyzed the Foxl2 gene of M. rohbrofa and found that the transcription factor it encodes is expressed in sperm cells in the testicles and oocytes in the ovary, and the expression is highest in the early stage of ovarian development (Stage I). This bisexual expression pattern suggests that Foxl2 may play a role in gonad development in both male and female, rather than just promoting ovarian differentiation (Xu et al., 2022). In some crustaceans (such as crayfish), genes such as Dmrt1 were also identified, which are highly expressed in male embryos and are inhibited in females. These findings suggest that crustaceans are likely to have a conserved gender-regulating gene network, including the IAG-led male pathway and the Foxl2/Dmrt-mediated gonad differentiation pathway, which interact together to determine the final gender phenotype. It should be noted that the gender determination patterns of different shrimp species vary. 4.3 Reproductive hormone signaling pathway and neuro-endocrine regulatory genes The reproduction process of shrimp is finely controlled by the endocrine system and involves multi-level regulation of the brain-stem-godal axis. Similar to the pituitary-godal axis of vertebrates, crustaceans have endocrine organs and hormones that correspond to their functional functions. The X-organ-sinus complex in the stalk of shrimp eye is equivalent to the endocrine center and secretes a variety of peptide hormones, one of which is the inhibitory hormone (GIH, also known as the gonadal inhibitory hormone). GIH belongs to the crustacean hyperglycemia hormone (CHH) family, which inhibits the development and maturation of female shrimp's ovaries. When the eye stalk removal (GIH source removal) is used in breeding production, the shrimp ovaries will mature quickly, which has long been applied to shrimp reproduction control. It can be seen that GIH and other eye stalk hormone genes play a negative switch role in reproductive regulation. At present, multiple member genes of the CHH superfamily of the Pacific white shrimp have been identified (such as CHH, MIH, VIH, etc.) and have demonstrated their function in stress metabolism and reproductive regulation (Wang et al., 2019). In addition to central hormones, the gonad itself secretes hormones that affect the reproductive process. The ovaries of female shrimps will produce steroid hormones such as Eksorbenzodione, which can promote ovarian development. In terms of neuromodulation, neurotransmitters such as somatostatin-like peptides and dopamine distributed in the brain and ganglion are believed to be involved in the regulation of reproductive signals. They indirectly affect the expression of gonad genes by regulating the secretion of upstream endocrine hormones. Molecular studies in recent years have also revealed the existence and role of reproductive-related hormone receptor genes. For example, receptor proteins and downstream signaling pathway genes of CHH family hormones have been identified in shrimp, which will trigger a series of transcriptional responses once activated.
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